Information about conditions and events in the ground may be of great value in relation to processes undertaken in the ground. For instance when trying to understand processes in a petroleum reservoir with the purpose of optimising the production or stimulation operations, it is vital to know physical conditions in the reservoir. The physical conditions may include pressure, temperature, location of seismic events, electric conductivity and other conditions that are well known to a person skilled in the art.
Some of these conditions may be retrieved with sufficient accuracy from the main wellbore, while others should be recovered from the formation away from the main wellbore. As in the case of seismic events, it is advantageous to have at least three geophones spaced out in the ground in order be able to interpolate where the seismic events occurred.
From GB 2370303 it is known to position sensors in abandoned boreholes. The deployment of equipment in such abandoned wellbores are difficult, because it is not deployed with the final completion pipe through the wellbore and connecting the wire to surface will be difficult.
This is particularly so in the event of registering seismic events as the attenuation rate in the formation of signals originating from such events is relatively large, and geo-phones are sensitive to unwanted noise, for instance from a flowing fluid such as fracturing fluid and proppant particles.